Induction of cytochrome P450 1A1 gene expression, oxidative stress, and genotoxicity by carbaryl acid thiabendazole in transfected human HepG2 and lymphoblastoid cells

Carbaryl and thiabendazole, two widely used pesticides, have been shown to induce cytochrome P450 1A1 (CYP1A1) expression, but neither compound is cap able of displacing [H-3] 2,3.7,8-tetrachlorodibenzo-P-dioxin from its aryl hydrocarbon receptor binding site. In the present study, we investigated th e transcriptional regulation of CYP1A1 as well as other genes in various hu man hepatoma HepG2 cell lines stably transfected with the chloramphenicol a cetyl transferase (CAT) reporter gene and cloned under the control of each of 14 promoters or response elements from relevant stress genes. Carbaryl a nd thiabendazole were found to activate CYP1A1 at the level of transcriptio n, as demonstrated by the dose-dependent increase in reporter CAT and CYP1A 1 mRNAs. Moreover, this effect appeared to be mediated via the xenobiotic r esponsive element (XRE), because both pesticides specifically activated var ious fusion constructs containing XRE sequences (CYP1A, glutathione S-trans ferase, and XRE). Carbaryl and to a lesser extent thiabendazole also activa ted other stress genes such as c-fos and NF-kappa BRE, HSP70 and GRP78, and GADD153 at a transcriptional level. These data suggest that these molecule s induce early alert genes, including those known to be sensitive to oxidat ive stress. This led us to examine the genotoxic effect of carbaryl and thi abendazole by an in vitro DNA repair solid-phase assay. Both compounds prov oked a strong DNA-damaging activity in the human lymphoblastoid cell line t hat constitutively expresses human CYP1A1 cDNA, but not in the parental lin e, indicating that CYP1A1 is chiefly implicated in carbaryl and thiabendazo le genotoxicity. This effect was confirmed on HepG2 cells. These observatio ns support the notion that intracellular signals leading to CYP1A1 inductio n, oxidative stress, and genotoxicity are intimately related. (C) 2001 Else vier Science Inc. All rights reserved.